Runway surveillance is very important for airport operation. Runways are continuously subjected to damages, such as potholes created as a result of wear and tear of aircraft or other vehicles using the runways. Occasionally, debris or foreign objects may occur on runways, which can be due to jet blast, aircraft take-off/landing, natural causes etc. On an active runway involving the movement of aircrafts, the presence of FOD may lead to an air crash and consequential loss of life resulting in significant losses to airline companies.
Different methods are employed to conduct runway surveillance: Conventionally, inspection officers move around the airport runways to conduct visual and manual surveillance, periodically. Visual inspection is slow, and labor intensive. Furthermore, visual inspection is unreliable as it is subjected to conditions surrounding the runway.
Some airports use automated systems employing radar to detect damages, debris and other hazards on an airport runway and its adjacent areas. In a system using radar, a microwave signal is usually transmitted over a runway and reflected signals from any foreign object are detected and analyzed. Since the microwave signals are pulsed or structured, the time taken for the signal to reach the receiver is calculated from which the distance to the foreign object is derived. By using radar sensors having smaller wavelengths and higher pulse repetition frequencies, it is possible to achieve higher resolution in range, which in turn, may reduce the background clutter.
However, a system using any radar for runway surveillance has its own limitations. While radar is an excellent means to detect metal objects, it is less sensitive in detecting non-metallic objects, such as rubber. Objects made of materials having poor radar signature (e.g. rubber) can cause major problems for such radar-based systems. Further, radar may not be relied upon for detecting smaller non-metallic objects. Further limitations include radar blind spots or shadows due to blockages caused by other objects or infrastructure. In addition, radar may trigger a false alarm by indicating a strong signal for signals reflected from even small metal objects that may not be so hazardous. A radar based surveillance system thus lacks “intelligence” and suffers from inability to provide visual image of the object for verification and characterization by the operator.
Some airports utilize infrared or thermal-imaging systems to detect objects, cracks voids etc. on a runway. However, systems employing infrared or thermal-imaging systems can only sense the infrared radiation (emitted from objects), which is outside the thermal equilibrium of the surroundings i.e. a infrared or a thermal imaging system can only detect objects (e.g. a piece of warm metal debris on a cool runway) which have sufficient thermal contrast. Small objects which have poor thermal contrast may pose significant challenges for infrared/thermal imaging system. Further, the performance of such systems is unpredictable under adverse weather (e.g. cold weather) conditions. In addition, infrared/thermal imaging systems also lack the resolution needed for object detection, characterization and classification.
Recently, surveillance using one or more video cameras placed near the runways has been proposed. Video signals obtained from the cameras are visually monitored by an operator on the console of an airport control room.
It has also been proposed to rely on image processing (e.g. background subtraction) to detect any FOD by processing video images of runways received from the surveillance cameras.
FOD detection using background subtraction has a number of problems. Firstly, the pixel properties are not always sufficient to discriminate correctly between the background and the foreground pixel. Furthermore, background is subjected to changes such as due to noise, clutter, extraneous events, variations in illumination conditions and weather conditions.
Furthermore, currently used image processing system is dependent on ambient lighting conditions and is not suitable for low lighting conditions, which causes significant problems in pixel characterization.
Video cameras used in existing surveillance systems require additional assisted illumination such as a laser light or infrared light for night surveillance. This, in turn, requires significant infrastructure in an airport using such a system, which increases cost. Also, the presence of an optical light such as a laser light or infrared light can interfere with other systems used in the airport, and may pose safety problems for navigation of aircrafts at the airport, and may pose a hazard to pilots etc.
Accordingly, there is a need to provide a runway surveillance, which seeks to address one or more of the above problems.